The present invention relates to an optical device for rerouting and modifying an optical signal, or more specifically, to an optical configuration including a diffraction grating that can be used for a dynamic gain equalizer and/or a configurable add/drop multiplexer.
In optical wavelength division multiplexed (WDM) communication systems, an optical waveguide simultaneously carries many different communication channels in light of different wavelengths. In WDM systems it is desirable to ensure that all channels have nearly equivalent power. To help achieve this, gain equalizers are disposed at various points throughout the system to control the relative power levels in respective channels. Dense WDM systems require special add/drop multiplexers (ADM) to add and drop particular channels (i.e., wavelengths). For example, at predetermined nodes in the system, optical signals of predetermined wavelength are dropped from the optical waveguide and others are added.
Typically, gain equalizing and add/drop multiplexer devices involve some form of multiplexing and demultiplexing to modify each individual channel of the telecommunication signal. In particular, it is common to provide a first diffraction grating for demultiplexing the optical signal and a second spatially separated diffraction grating for multiplexing the optical signal after it has been modified. An example of the latter is disclosed in U.S. Pat. No. 5,414,540, incorporated herein by reference. However, in such instances it is necessary to provide and accurately align two matching diffraction gratings and at least two matching lenses. This is a significant limitation of prior art devices.
To overcome this limitation, other prior art devices have opted to provide a single diffraction grating that is used to demultiplex an optical signal in a first pass through the optics and multiplex the optical signal in a second pass through the optics. For example, U.S. Pat. Nos. 5,233,405, 5,526,155, 5,745,271, 5,936,752 and 5,960,133, which are incorporated herein by reference, disclose such devices.
However, none of these prior art devices disclose an optical arrangement suitable for both dynamic gain equalizer (DGE) and configurable optical add/drop multiplexer (COADM) applications. In particular, none of these prior art devices recognize the advantages of providing a simple, symmetrical optical arrangement suitable for use with various switching/attenuating means.
Moreover, none of the prior art devices disclose a multiplexing/demultiplexing optical arrangement that is compact and compatible with a plurality of parallel input/output optical waveguides.
For example, U.S. Pat. No. 5,414,540 to Patel et al. discloses a liquid crystal optical switch for switching an input optical signal to selected output channels. The switch includes a diffraction grating, a liquid crystal modulator, and a polarization dispersive element. In one embodiment, Patel et al. suggest extending the 1xc3x972 switch to a 2xc3x972 drop-add circuit and using a reflector. However, the disclosed device is limited in that the add/drop beams of light are angularly displaced relative to the input/output beams of light. This angular displacement is disadvantageous with respect to coupling the add/drop and/or input/output beams of light into parallel optical waveguides, in addition to the additional angular alignment required for the input beam of light.
With respect to compactness, prior art devices have been limited to an excessively long and linear configurations, wherein the input beam of light passes through each optical component sequentially before being reflected in a substantially backwards direction. U.S. Pat. No. 6,081,331 discloses an optical device that uses a concave mirror for multiple reflections as an alternative to using two lenses or a double pass through one lens. However, the device disclosed therein only accommodates a single pass through the diffraction grating and does not realize the advantages of the instant invention.
It is an object of this invention to provide an optical system including a diffraction grating that is relatively compact.
It is a further object of the instant invention to provide an optical configuration for rerouting and modifying an optical signal that can be used as a dynamic gain equalizer and/or configurable add/drop multiplexer.
The instant invention provides a 4-f optical system comprising a dispersive element for spatially separating an input optical signal into different spectral channels and a modifying array for selectively modifying each of the different spectral channels. At least one element having optical power, such as a lens or a spherical mirror, provides optical communication between the dispersive element and the modifying array.
Conveniently and advantageously, the dispersive element and the modifying array are disposed substantially at a focal plane of the at least one element having optical power. Moreover, the dispersive element and element having optical power are used in a first and a second pass through the optics, thus obviating the requirement of providing matching elements.
In accordance with the instant invention there is provided an optical device comprising: a first port for launching a beam of light; first redirecting means disposed substantially one focal length away from the first port for receiving the beam of light, the first redirecting means having optical power; a dispersive element disposed substantially one focal length away from the first redirecting means for dispersing the beam of light into a plurality of sub-beams of light; second redirecting means disposed substantially one focal length away from the dispersive element for receiving the dispersed beam of light, the second redirecting means having optical power; and, modifying means optically disposed substantially one focal length away from the second redirecting means for selectively modifying each sub-beam of light and for reflecting each of the modified sub-beams back to the second redirecting means, wherein each sub-beam of light is incident on and reflected from the modifying means along substantially parallel optical paths.
In accordance with the instant invention there is provided an optical device for rerouting and modifying an optical signal comprising: a first port for launching a beam of light; a concave reflector having a focal plane for receiving a beam of light launched from the first port; a dispersive element disposed substantially at the focal plane for spatially dispersing a beam of light reflected by the concave reflector and for redirecting a spatially dispersed beam of light back to the concave reflector; and modifying means disposed substantially at the focal plane for modifying the spatially dispersed beam of light reflected by the concave reflector and for reflecting the modified spatially dispersed beam of light back to one of the first port and a second port via the concave reflector and the dispersive element.
In accordance with the instant invention there is further provided a method of rerouting and modifying an optical signal comprising the steps of: launching a beam of light towards an element having optical power off an optical axis thereof; redirecting the beam of light incident on the element having optical power to a dispersive element disposed substantially one focal length away from the element having optical power; spatially dispersing the redirected beam of light into a plurality of different sub-beams of light corresponding to a plurality of different spectral channels with a dispersive element disposed substantially one focal length away from the element having optical power; redirecting the plurality of different sub-beams of light to a modifying means optically disposed substantially two focal lengths away from the dispersive element; selectively modifying the plurality of different sub-beams of light and reflecting them in a substantially backwards direction; and redirecting the selectively modified plurality of different sub-beams to the dispersive element and combining them to form a single output beam of light, wherein the plurality of different sub-beams of light and the selectively modified plurality of different sub-beams follow substantially parallel optical paths to and from the modifying means, respectively.
In accordance with the instant invention there is provided an optical device for rerouting and modifying an optical signal comprising: a lens including a first end having a single port coincident with an optical axis thereof and a second end having two ports disposed off the optical axis; an element having optical power disposed about one focal length away from the lens for receiving a beam of light launched from the single port; a dispersive element disposed about one focal length away from the element having optical power for spatially dispersing a beam of light received therefrom; and modifying means optically disposed about two focal lengths away from the dispersive element for modifying and reflecting a beam of light spatially dispersed by the dispersive element, wherein said one focal length is a focal length of the element having optical power.
In accordance with the instant invention there is provided a method of modifying and rerouting a beam of light comprising the steps of: launching the beam of light through a first port disposed about a first end of a lens off the optical axis of the lens, the beam of light launched in a direction parallel to the optical axis; allowing the beam of light to pass through the lens to a single port disposed about an opposite side of the lens coincident with the optical axis, and allowing the beam of light to exit the single port at a first predetermined angle to the optical axis; modifying the beam of light and reflecting the modified beam of light back to the single port at a second predetermined angle to the optical axis; and, allowing the modified beam of light to pass through the lens to a second port disposed about the first end of the lens, the second port disposed off the optical axis and spatially separated from the first port.